©2012 This excerpt is taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 12, December 2012.
By Prem Mehrotra, P.E., Life Member ASHRAE
About the Author
Prem Mehrotra is president of General Energy Corp., in Oak Park, Ill.
The Evelyn Pease Tyner Interpretive Center (EPTIC) at Air Station Prairie in Glenview, Ill., includes exhibits and a learning center to help visitors understand the ecology of local prairies. The building is about 3,000 ft2 (279 m2) in net area and is located on the southeast corner of 32.5 acre remnant of a tall grass prairie.
The conceptual design process was begun in 2004. The project was inspired by Evelyn Pease Tyner, a local environmentalist and conservationist, and the facility. All the building systems, including construction materials and processes, were planned to harmonize with nature. The team of architect, engineers, owner, and all the stake holders met for several years on a regular basis. As the project evolved, the objective became to make the building self-sustaining for its energy use.
The final design target was LEED Platinum certification and to use solar energy to power building systems. The project was somewhat delayed to acquire additional funds, and to obtain renewable energy grants.
The design engineers focused on maximizing LEED points for water efficiency, energy and atmosphere, and indoor environment. The architectural firm used exterior spaces for exhibits. This decision helped reduce the building’s overall size, which created a smaller internal volume and helped contain costs and minimize the energy footprint.
Orientation & Natural Ventilation
The building has an east/west orientation, and the solar gain was offset using large overhanging eaves on the south-facing façade and minimal eaves to the north. The 20 ft (6 m) high windows provide visitors incredible views of the prairie and allows for daylighting, saving energy. Operable windows in every space allow prevailing breezes to ameliorate temperatures without using energy. Careful attention to cross ventilation design means that the building is comfortable in the summer without mechanical systems running, despite being completely exposed on the prairie.
Two-thirds of the roof is vegetated with the other one-third used for photovoltaic panels. The roof has an R-value of 38. The walls are designed with a U-value of 0.039. A window shading coefficient of 0.25 is used.
Geothermal Heat Pumps
Two geothermal heat-pumps are used for air-conditioning of the entire building. A typical heat pump system (Figure 1) has a cooling efficiency rating of 15.39 EER or 0.78 kW/ton and heating efficiency rating of 4.45 COP. The geothermal heat pumps were sized to meet the winter heating load to ensure that supplemental heating is not required during the winter. In the Chicago metropolitan area, heating requirements govern the size of heat pumps. Therefore, the project uses energy recovery ventilators (ERVs) to reduce the size of the heat pumps.
ERVs recover heat from exhaust air to preheat outside air during winter and precool outside air during summer before introducing the air to the heat pumps for mixing with return air. This helped reduce the size of the heat pumps, eliminated reheating requirements, and reduced the size of the geothermal loop. The heat recovery units are rated at 60% efficiency. Value engineering was an ongoing process during the design phase to stay within budget.
Lighting and Daylighting
Every space within the building is lit with natural daylight and has a view to the prairie. Because of the amount of natural daylight in the building, electricity consumption for the lighting system is minimized.
The display cases and shelves embedded within the façade are transparent, allowing sunlight to penetrate. Also, visitors can see through the display and into the building.
The lighting in the learning center consists of indirect light with metal halide lamps. The metal halide lamps have two-step controls that use solar light sensors. The rest of the areas are provided with T8 lamps and electronic ballasts controlled by occupancy sensors. Outdoor spotlights are used to illuminate the exhibits to prevent direct proliferation of light to the dark sky. Solar bollards powered by solar light are used to illuminate the walkway to the building from the roadside.
Citation: ASHRAE Journal, vol. 54, no. 12, December 2012
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